What wavelength, spot size, and power? These all dictate what type of sensor is needed. (i.e. photodiodes may not respond well or at all to IR radiation)
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
650nm, Spot? .125 spot, and power I am not too sure about. Photodiodes are like 4 bucks each. Thats a little high for me. LDR's can be cheap, but I am concerned about their dissipation rate.
Should be able to get photodiodes for easily under a buck, check Allied or Newark. If I recall, LED's also respond to light, you may want to try experiementing with a RED one.
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
With specifications and desired operation details, I'm sure many of us here would be glad to point you in the right direction or come up with a solution. Is this a homework assignment?
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
I want to be able to determine how long my sensor is blocked. So for starters, I need to know what type of sensor to use. You suggested a photodiode so I will look into that (thanks). Next I need to know how to wire it so that ambient fluctuation does not interfer with my readings. I just want to know if the laser is blocked and for how long.
For speed, you want to reverse bias the photodiode- this reduces the junction capacitance. The diode then generates a current proportional to light intensity (until saturation). You then need a current-to-voltage converter circuit (think high speed op amp). Follow this with a high speed buffer or TTL driver (schmitt?) to interface to the digital input on the I/O card. Suspect that diode responce will be way faster (10's of nsec, depending on photodiode size and capacitance) than your software (10's of msec). Suggest a narrow bandpass filter to only allow your laser wavelength to get through to the detector.
Hamamatsu, a major manufacturer of photodiodes has some good app notes, here are some links to get you rolling:
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
Thanks for the head start. If you know anyone that would like to draw up the circuit, let me know. It started out as a simple circuit, (it probably still is), but I am sure I will need help. The schematics you linked me to will be very helpful.
The best way to reject the ambient is to modulate the light source with a -- relative high -- frequency and
use selective amplifier. Radio Schack had a 40kHz
receiver module years ago.
